Electronic time delay circuit



March 1, 1949. E. D. SCHNEIDER ET AL 2,463,318

ELECTRONIC TIME DELAY CIRCUIT Filed Aug. 5, 1944 l3- I? 4 12% Z 25 --o M27 E g zs Inventers:

Elbert 'D. Schneider, Fao-Hsiung Chin,

Patented Mar. 1, 1949 ELECTRONIC TIME DELAY CIRCUIT Elbert D. Schneider, Scoiia,

Chin, Schenectady,

and Pao-Hsiung N. Y., assignors to General Electric Company, a. corporation of New York Application August 5, 1944, Serial No. 548,164

2 Claims. 1

Our invention relates to electric valve circuits and more particularly to improved electric valve circuits for effecting a circuit controlling operation with a predetermined time delay.

Electronic timing circuits have been widely used in industrial applications to effect a desired control at the end of a predetermined time interval. One circuit of this type is described and claimed in Schneider Patent No. 2,171,347, dated July 24, 1937, and assigned to the assignee of the present application. While these timers have been satisfactory in many applications, it has been found that fluctuations of the voltage supply decrease the accuracy of the timing intervals. Supply voltage fluctuations also tend to cause faulty operation, such as chattering of the relay at or near the end of the timing interval. In accordance with the teachings of the present invention, improved electronic timing circuits are provided particularly adapted for energization from an alternating current circuit and with which consistent timing is obtained despite fluctuations of the supply circuit voltage.

It is an object of our invention to provide a new and improved electronic time delay circuit.

It is another object of our invention to provide a new and improved electronic time delay circuit which provides consistent operation regardless of fluctuations in the voltage of the supply circuit.

In accordance with one illustrated embodiment of our invention, we provide a new and improved alternating current electronc time delay relay in which a timing capacitor is charged through the grid-to-cathode circuit of a high vacuum discharge device of the pentode type, and in which the interval of time delay is initiated by closure of a switch in the cathode lead of the discharge device, the device being maintained substantially non-conducting for an interval determined by the discharge of the capacitor through a parallel resistor. A voltage divider connected across the alternating current supply circuit determines the level of voltage to which the timing capacitor is charged and also provides an alternating current component of voltage for biasing the control grid of the discharge device and for energizing the screen grid of the discharge device. A voltage regulating or glow discharge tube is connected across a portion of the voltage divider to regulate the volt age to which the timing capacitor charges and to provide fiat topped alternating voltages having a predetermined maximum amplitude for energizing the screen grid and for the alternating current bias of the control grid.

For a better understanding of our invention, reference may be had to the following description taken in connection with the accompanying drawing, and its scope will be pointed out in the pacitor 22.

2 appended claims. In the drawing, Fig. 1 is a schematic representation of one embodiment of our invention; Fig. 2 is a schematic representation of another embodiment of our invention; and Fig. 3 is a schematic representation of still another modification.

Referring now to Fig. 1 of the drawing, we have shown our invention embodied in a circuit for energizing the operating coil l of an electromagnetic relay 2 at the end of a predetermined interval of time after the closure of an initiating switch 3. Energization of the operating coil I from an alternating current supply circuit 4 is controlled by the conduction of an electric discharge device 6 which, in the preferred form shown in the drawing, is a high vacuum valve of the pentode type having an anode 'l, a cathode 8, a control member or grid 9, a screen grid 10 and a suppressor grid ii. The cathode of the electric valve 6 is connected with one of the alternating current supply lines 4 through the initiating switch 3, and the anode l is connected with the other alternating current supply line through the operating coil 1 of the relay 2. A resistor I2 and capacitor iii are connected in series and across the terminals of the operating coil to provide an energy storage circuit for maintaining the operating coil l energized during alternate half cycles of the supply circuit voltage during which the electric valve 6 is nonconducting. In order to provide the energizing voltages for the control member 9 and the screen grid ill, a voltage divider including resistors i i-ll, inclusive, is connected across the alternating current supply 4. The control member or grid 9 is connected with an adjustable point on resistor [6 by a movable contact l3 through a circuit including a timing capacitor is and a parallel connected discharge resistor 29. The screen grid 10 of the discharge device 5 is maintained at a voltage intermediate the common terminal of resistors i4 and i5 and to the lower alternating current supply line 1 by a voltage dividing circuit including a series connected resistor 2| and ca- The screen grid is connected to the common terminal of resistor 2i and capacitor 22. This circuit impresses a voltage on the screen grid which is slightly lagging in phase with respect to the voltage impressed on the voltage divider including resistors i l-ll, inclusive. This voltage relation has been found desirable as contributing to the consistent operation of the timer. A resistor 23 is connected from the cathode of the electric valve 5 to a point of voltage between the voltage dividing resistor 15 and the upper terminal or resistor M and, as illustrated, is connected to the juncture of resistors l4 and 15. In accordance with an important aspect of the present invention, a voltage regulating device, such as a glow discharge valve 24 having a predetermined of resistor l6.

minimum ionization voltage, is connected between the juncture of resistors l4 and I5 and the lower alternating current supply line 4. When connected in this manner, the device 24 serves to regulate the voltage to which the capacitor 59 is charged, as well as to provide flat topped alternating voltages of predetermined regulated amplitude on the control grid -9 and the screen grid IE. Since the characteristics of the pentode valve 6 are such that the current conducted is substantially independent of supply line voltage fluctuations when the voltage of the screen grid is maintained constant, this combination makes it unnecessary to regulate the anode voltage of valve 9 and in this way minimizes the currentcarrying duty imposed on regulating valve 24.

The relay 2 may be employed to control any desired number of circuits and, as illustrated, is provided with a normally open contact 25 and a normally closed contact 26 connected in circuit with load conductors 21 and 28, respectively.-

The features and advantages of the present invention will become more apparent from a consideration of the operation of the embodiment illustrated in Fig. 1. With initiating switch 3 in the open position, as illustrated, and the supply conductors 4 energized with an alternating current voltage, a charging circuit for the capacitor 19 is established across the portion of the voltage divider of which the voltage is regulated by the glow discharge device 24. This charging circuit is traced from the lower conductor 4 through resistor ll, lower portion of potentiometer l8, capacitor iii-resistor 20 network, grid S-cathode B path, resistor 23 to junction of resistors I4 and i5. Thus the capacitor charges, with the plate nearest control grid 9 negative, to a Voltage determined by the voltage of the common terminal of resistors 14 and [5. Since this voltage is regulated by the gaseous discharge device 24,

the voltage to which the timing capacitor I9 is charged is also regulated. During this time the anode-cathode voltage impressed on the discharge valve 6 is that appearing across resistor 14. This is insufiicient to pick up the relay 2 and as a result the relay remains deenergized as long as the initiating switch 3 is open. Upon closure of initiating switch 3, the anode-cathode circuit of "discharge device 6 is connected across the alternating current supply conductors 3 and the gridto-cathode circuit of the valve is completed to include an alternating current bias voltage appearing across resistor IT and the lower portion This voltage is substantially in phase with the anode-cathode voltage impressed on the discharge device 6 and is of flat topped wave form due to the connection of the glow discharge device 24 across voltage dividing resistors IE-ll, inclusive. The magnitude of the alternating current bias may be adjusted by adjusting the slider on resistor ll. This bias voltage is opposed by the transient voltage of the timing capacitor H] which is not further charged after closure of initiating switch 3 and which continues to discharge through resistor 26. At a predetermined time after closure of switch 3,

the voltage of capacitor l9 reduces to the point where the valve 6 conducts sufficiently to pick up the relay 2. As has been pointed out, the flat topped alternating bias voltage is regulated by discharge device 24 and the voltage to which capacitor I9 is charged is regulated by this discharge device so that the time required for the voltage of control member 9 to reach a predetermined value is independent of supply line voltage fluctuations. By the employment of a pentode-type electric valve having its screen grid maintained at a constant voltage, the current conducted by the device is substantially independent of the anode-cathode voltage. Therefore, the interval or" time required for actuation 0t relay 2 is substantially independent of supply line voltage fluctuations with the regulating arrangement disclosed in Fi 1. In the particular arrangement illustrated, the phase of the voltage of the screen grid is retarded with respect to the plate voltage of valve 6. It has been found that this shirt in phase of the screen grid voltage increases the consistency of the timing operation with variable supply voltage.

In Fig. 2 we have illustrated a modification of our invention which is in general similar to the arrangement of Fig. 1, but in which the relay is normally in its actuated position and is deenergized for a predetermined interval upon closure of the initiating switch. When the relay is reset by opening of the initiating switch, the relay is again energized. In the drawing, elements corresponding to elements of Fig. 1 have been designated by the same reference numerals. It will be noted that in Fig. 2 the resistor 23 has been omitted and that the initiating switch is not connected in the cathode lead of the valve 6, but rather in circuit with the Voltage dividing resistors i l-ll between the resistor l1 and the alternating current supply conductor 6 which is connected with the cathode of the discharge device 6. The initiating switch has been designated 3'. With this arrangement, it will be noted that the anode-cathode circuit of discharge device 6 is not interrupted by opening of the initiating switch and for this reason the relay 2 is actuated before closure of the initiating switch. In the arrangement shown in Fig. 1 the timing capacitor [9 is charged to the Voltage appearing across voltage dividing resistor 15 and the upper portion of resistor [6. In the arrangement shown in Fig. 2 the capacitor [9 charges to the voltage appearing between the common terminal of resistors l4 and i5 and the alternating current supply conductor 4 connected with the cathode of valve 6. When the initiating switch is closed, a regulated fiat topped alternating current bias appearing across resistor ll and the lower portion of resistor I6 is impressed on the control member 9 in series with the transient voltage of thetiming capacitor l9 in the same manner as it is in the arrangement ofFig. 1. From this description, it is apparent that except for the sequence of relay operations accomplished, the operation of the circuit of the embodiment illustrated in Fig. 2 is essentially the same as that illustrated in Fig. 1,

The arrangement shown in Fig. 3 is similar to that illustrated in Fig. 2 but the relay is operated in accordance with the conduction of a gaseous discharge amplifier valve controlled by the valve '5. In Fig. 3 numerals corresponding to those nected through the relay coil 1 and the parallel resistor and capacitors l2 and 13, respectively, to the juncture of voltage dividing resistor l1 and the initiating switch '3'. The electric valve 29 is preferably of the gaseous discharge type and is provided with a control member v30 connected "to'the anode'circuit of the electric valve '6 through a current limiting resistor 31. A suitable filter capacitor 32 is connected between the control member and cathode of the valve 29. A parallel connected resistor 33 and capacitor are connected in the anode circuit of electric valve 6 in place of the relay coil i and its parallel connected capacitor it. This arrangement provides advantages of a vacuum tube relay and at the same time permits the operation of an electromechanical relay having larger current requirements.

The operation of the embodiment illustrated in Fig. 3 is believed to be apparent from the detailed description of the operation of the arrangement of Fig. 2. The state of conduction of the electric valve 6 is the same for these two ar-- rangements and the conductivity of the gaseous discharge valve 29 is decreased as the conductivity of valve 6 increases. In other words, the electromagnetic relay 2 of the arrangement illustrated in Fig. 3 will be in the opposite operative position at any instant as compared with the relay of Fig. 2. This is apparent from an inspection of the rawing in which it will be noted that the greater the conductivity of valve 6, the greater the negative bias impressed on control member 39 by resistor 33.

While we have shown and described particular embodiments of our invention, it will be obvious to those skilled in the art that changes and modifications may be made without departing from our invention in its broader aspects, and, we, therefore, aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States, is:

1. In combination, an alternating current supply circuit, a voltage divider connected across said supply circuit, an electric valve of the high vacuum type including an anode, a cathode, and a control grid, a screen grid, a capacitor, means for charging said capacitor from a portion of the voltage of said voltage divider including the internal control grid-to-cathode circuit of said electric valve, means including an initiating switch operable to its open position to interrupt the external control grid-to-cathode circuit of said valve and operable to its closed position to complete said external circuit and to include said capacitor and a portion of said voltage divider to control conduction by said electric valve in accordance with the transient voltage of said capacitor, voltage regulating means connected across a portion of said voltage divider to regulate the voltage to which said capacitor charges and to provide a fiat topped voltage across the portion of said voltage divider connected in the external control grid-to-cathode circuit of said valve to render conduction by said electric valve substantially independent of voltage variations of said supply circuit and means for supplying to said screen grid a periodically varying voltage that is dephased with respect to the voltage supplied to said control grid comprising a resistancereactance phase shifting network supplied from said voltage divider and a connection from said screen grid to said network.

2. In combination, a supply circuit, a voltage divider connected across said supply circuit, an electric valve of the high vacuum type including an anode, a cathode, a screen grid and a control grid, means for connecting the anode-cathode circuit for energization from said supply circuit, a capacitor, means for establishing a charging circuit for said capacitor including at least a portion of said voltage divider, a discharge circuit for said capacitor, initiating means including a switch operable to its open position to interrupt the external control grid-to-cathode circuit of said valve and operable to its closed position to complete said external circuit to initiate a timing interval determined by the discharge of said capacitor, voltage regulating means including a glow discharge device connected across a portion of said voltage divider to regulate the voltage to which said capacitor charges and to regulate the voltage across the portion of the voltage divider included in the external control grid-tocathode circuit of said valve and means for supplying to said screen grid a periodically varying voltage having a lagging phase displacement with respect to the voltage of said control grid comprising a resistor and a capacitor connected in series across said portion of said voltage divider.

ELBERT D. SCHNEIDER. PAO-I-ISIUNG CHIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,171,347 Schneider Aug. 29, 1939 2,203,468 Martin June 4, 1940 2,216,232 Dow Oct. 1, 1940 2,251,263 Schoene Aug. 5, 1941 2,274,158 Penther Feb. 24, 1942 2,301,195 Bradford Nov. 10, 1942 2,313,918 Brownlee Mar. 16, 1943 2,337,905 Livingston Dec. 28, 19-43 2,359,080 Bivins Sept. 26, 1944 

